Ratchet type selector switches



July 30, 1963 B. J. WARMAN RATCHET TYPE SELECTOR SWITCHES Filed Feb. 18,1960 United States Patent 3,099,757 RATQHET TYPE SELECTQR SWITCIESBloomfield James Warman, London, England, assiguor to AssociatedElectrical Industries Limited, London, England, a British company FiledFeb. 18, 1960, Ser. No. 9,475 Claims priority, application Great BritainFeb. 26, 1959 2 Claims. (Cl. 307--141.4)

This invention relates to selector switches of the ratchet operated kindsuch as are used as single-motion or twomotion selectors in automatictelephone exchange systems and elsewhere.

Basically a ratchet switch includes an electromagnetically operatedratchet and pawl mechanism which moves the switch one step forward foreach energization (or deenergization) of an eleotromagnet energizingcoil of the switch. In order to give the ratchet switch a self-driveaction, requiring alternate energization and de-energiz-ation of theope-rating coil, the switch is also commonly provided with interruptercontacts which are connected in the energizing circuit for the coil andon energization of the coil are opened to break the energizing circuit.The consequent de-energization of the coil results in reclosure of theinterrupter contacts, with consequent reenergization of the coilprovided that the energizing circuit remains otherwise complete. Theinterrupter contacts have the disadvantage of requiring carefuladjustment and of being liable, due to wear, to give trouble or at leastto require increased maintenance attention.

According to the invention the interrupter contacts of a ratchetselector switch are replaced, in a stepping circuit for the switch, by atransistor which has the energizing coil of the switch magnet connectedin its collectoremitter circuit and which is connected as a blockingoscillator by virtue of a regenerative feedback coupling providedbetween its collector-emitter circuit and its base circuit. Preferablythe regenerative coupling is provided by means of a feedback coilmagnetically coupled with the energizing coil of the switch.

The invention may be better understood by consideration of theaccompanying drawing the single figure of which illustrates for asingle-motion ratchet switch a stepping circuit which permits the switchto be pulsedriven or effectively self-driven.

Referring to the drawing a ratchet switch RS is shown in conventionalmanner as having two contact banks All and A2 (of which A2 is a controlbank) with associated wipers W1 and W2 which are driven by means of aratchet and pawl mechanism (not shown) under control of an electromagnetDM. It is assumed that in order to step the wipers W1 and W2 by onestep, the electromagnet DM requires to be energized and thende-energized. The electromagnet DM has two magnetically coupled coils c1and c2 of the which 01 is the enengizing coil and 02 is a feedback coil.The energizing coil c1 is connected in the collector-emitter circuit of1a transistor T and the feedback coil 02 is connected in the basecircuit of the transistor between the base and a source of positive biaspotential The magnetic coupling between the coils c1 and c2 affords aregenerative feedback from the transistor emitter-collector circuit toits base circuit but the positive bias on the base normally preventsoscillatory action by preventing conduction of the transistor. Anegative-going stepping pulse P applied to the base of the transistor Tby way of a capacitance coupling network C, R and an appropriately poledrectifier Rf will tend to cause conduction of the transistor. consequentcurrent flow in the switch coil 01 initiates a regenerative actionthrough the feedback coil 02. The current flow through the transistortherefore rapidly increases and the magnetic flux induced by theenergizing coil 01 and linking the feedback coil 02 builds up tosaturation. On reaching satunation the regenerative action ceases andthe transistor becomes blocked off, that is non-conducting, until theflux has died away. Since the energizing coil 01 has now been energizedand then deenergized again, the ratchet switch RS is therefore caused tostep once.

If, instead of and as distinct from a stepping pulse P, a continuousnegative direct current potential is applied to the transistor base overa base connection lead I, then a blocking oscillator action similar tothat just described but continuously repeated can be obtained, thusimparting an effective self-driving action by which the switch isrepeatedly stepped until the negative bias on lead I is removed. Byarranging that this negative potential is applied from a control contactbank of the switch, constituting a testing or homing bank, a hunting orhoming action can be obtained in a manner readily apparent to oneskilled in the automatic telephone art. For example, in the drawing thebase connection lead I is shown included in a base circuit (independentof that including the feedback coil 02) in which it is connected througha resistor R1 and starting contacts st to the wiper of control bank A2of the switch RS, this are being used as a marking bank.

The home contact h of the control bank A2 is conneoted to negativebattery over normally-closed contact sh and the other contacts 1 0 ofthe bank are each selectively connected, by change-over switch m1 m0,either to negative battery or to earth. On closure of contact st thenegative potential appearing at contact h of control bank A2 starts theself-driving action already described, this action continuing as thewiper W2 passes over those contacts 1, 2, 3 which also have a negativepotential applied to them by their respective switches ml, m2, m3 Theself-drive action is stopped at the bank contact, e.g. contact 5, whichhas been marked by operation of the relevant switch (m5) to apply earthpotential to that contact instead of the negative potential. Asubsequent homing action can be achieved by a similar self-drive actioninitiated by restoring contact m5 and opening contact sh. Theseprovisions for self-driving action may be made either instead of or inaddition to the provisions for single'step operation.

Since the transistor can induce significant gain, the operation of theratchet switch can be controlled from a low power source which may beswitched electronically rather than mechanically or electromechanically,for instance by means of transistor binary pairs. Furthermore in thecase of single-step operation, the stepping action can be effected by ashort duration pulse P such as may be obtained from an electronic orferrite core gate circuit. The stepping circuit is therefore speciallysuited to electronic control. It may also be observed that the path overwhich the operating signal, as constituted by the stepping pulse P orthe negative bias on lead I as the case may be, is applied, includesneither the switch energizing coil nor the feedback coil. Since theoperating signal path can therefore be non-inductive, it can ifnecessary be of considerable length and may be run in a cable withoutcausing radiation or interference: moreover in deriving the bias forself-drive operation from a marking contact bank such as A2 of theswitch, the wiper (W2) of this contact bank need not be a bridging wiperbut can be of a nonbridging kind.

What I claim is:

1. In combination:

a source of continuous potential;

a ratchet operated selector switch including a plurality of contactbanks each having a first contact and succeeding contacts at least oneof which contacts is marked by the absence of said potential, saidcontact banks having thereon cooperating wipers, said contact banksincluding a control bank;

a ratchet operating electromagnet for effecting actuation of saidwipers, said electromagnet having an energizing coil therefor;

transistor blocking oscillator constituting a stepping circuit for saidwipers and comprising a transistor having a collector-emitter circuitincluding said energizing coil, a base circuit including regenerativefeedback means from said collector-emitter circuit, and a furtherindependent base circuit including a base connection to the wiper ofsaid control bank;

and means for applying to said first contact when 2. In combination: asource of continuous potential; a ratchet operated selector switchincluding a plurality of contact banks with cooperating wipers, saidcontact banks including a control bank, and in which said banks eachhave a first contact and succeeding contacts at least one of which ismarked by the absence of said potential thereon;

a ratchet operating electronragnet for effecting actuation of saidwipers, said electromagnet having an energizing coil therefor and afurther coil magnetically coupled with the energizing coil;

a transistor blocking oscillator constituting a stepping circuit forsaid wipers and comprising a transistor having a collector-emittercircuit including said enerlgizing coil, a base circuit including saidfurther coil connected as a regenerative feedback means from saidcollector-emitter circuit, and a further independent base circuitincluding a base connetcion to the wiper of said control bank;

and means for applying to said first contact when initially engaged bythe wiper of the respective control bank and to said number ofsucceeding contacts therein said continuous potential from said sourceover said wiper and base connection to initiate conduction of thetransistor and to effect a resultant sequence of blocking oscillatoractions in said transistor blocking oscillator by which theelectromagnet energizing coil is repeatedly energized with resultantstepping of the selector switch until the control bank wiper reachessaid contact marked by the absence of said potential.

References Cited in the file of this patent UNITED STATES PATENTS2,318,204 Deakin May 4, 1943 2,584,990 Dimond Feb. 12, 1952 2,801,374Svala July 30, 1957 3,018,419 B01111 Jan. 23, 196-2

1. IN COMBINATION: A SOURCE OF CONTINUOUS POTENTIAL; A RATCHET OPERATEDSELECTOR SWITCH INCLUDING A PLURALITY OF CONTACT BANKS EACH HAVING AFIRST CONTACT AND SUCCEEDING CONTACTS AT LEAST ONE OF WHICH CONTACTS ISMARKED BY THE ABSENCE OF SAID POTENTIAL, SAID CONTACT BANKS HAVINGTHEREON COOPERATING WIPERS, SAID CONTACT BANKS INCLUDING A CONTROL BANK;A RATCHET OPERATING ELECTROMAGNET FOR EFFECTING ACTUATION OF SAIDWIPERS, SAID ELECTROMAGNET HAVING AN ENERGIZING COIL THEREFOR; ATRANSISTOR BLOCKING OSCILLATOR CONSTITUTING A STEPPING CIRCUIT FOR SAIDWIPERS AND COMPRISING A TRANSISTOR HAVING A COLLECTOR-EMITTER CIRCUITINCLUDING SAID ENERGIZING COIL, A BASE CIRCUIT INCLUDING REGENERATIVEFEEDBACK MEANS FROM SAID COLLECTOR-EMITTER CIRCUIT, AND A FURTHERINDEPENDENT BASE CIRCUIT INCLUDING A BASE CONNECTION TO THE WIPER OFSAID CONTROL BANK; AND MEANS FOR APPLYING TO SAID FIRST CONTACT WHENINITIALLY ENGAGED BY THE WIPER OF THE RESPECTIVE CONTROL BANK AND TOSAID NUMBER OF SUCCEEDING CONTACTS THEREIN SAID CONTINUOUS POTENTIALFROM SAID SOURCE OVER SAID WIPER AND BASE CONNECTION TO INITIATECONDUCTION OF THE TRANSISTOR AND TO EFFECT A RESULTANT SEQUENCE OFBLOCKING OSCILLATOR ACTIONS IN SAID TRANSISTOR BLOCKING OSCILLATOR BYWHICH THE ELECTROMAGNET ENERGIZING COIL IS REPEATEDLY ENERGIZED WITHRESULTANT STEPPING OF THE SELECTOR SWITCH UNTIL THE CONTROL BANK WIPERREACHES SAID CONTACT MARKED BY THE ABSENCE OF SAID POTENTIAL.